Hydrological Modeling in the Upper Lancang-Mekong River Basin Using Global and Regional Gridded Meteorological Re-Analyses

Round 1

Reviewer 1 Report

This paper presents the results of testing the utility of two different gridded meteorological reanalyses in predicting hydrologic variables for the upper Lancang-Mekong River basin.  The research represents an ambitious use of “big data” and reveals some of the challenges currently faced by models that use global datasets. The paper is well organized and well written, the tables and figures are appropriate, and I believe the research will make a fine contribution to the literature.  A basic challenge is that the basin is huge, topographically and hydrologically diverse and spans areas affected by different sources of highly variable monsoonal moisture. Not surprisingly, precipitation and aspects of temperature are not handled well by the two datasets and there are notable differences between the upper and lower parts of this huge, elongate basin. The differences in “present” models suggest that both the datasets and models need to be better calibrated before they are used for future predictions.

As I note below, the manuscript lacks process-based explanations in the discussion: what do the results mean in terms of model success and weakness?   As written the sections of discussion mainly repeat what the reader has learned already from the results—there are serious differences in the two reanalyses and they make model results uncertain at best. I have made many comments/suggestions and minor corrections in the .pdf version of the manuscript, which I am attaching.  I list below several of the more important topics that need to be addressed, in no particular order.

1.    Timescale is extremely important in these analyses. The authors mention flows at different time scales (Peak; Daily; Yearly?) but eventually seem to use monthly (?) values.  They need to alert their readers early about time.

2.    The comparison dataset(s) seem to be from a downstream gage, but much could be learned by dividing this elongate basin into 3 (?) parts.  Are there upstream gages?  Do the reanalyses work better for more limited, hydrologically similar areas? These may be topics for future research, but perhaps some of the sources cited have already shown better performance at a more local scale?

3.    The basis of the CFSR data set is nearly a decade before the most rapid global warming.   How does this affect the results of the reanalysis and model tuning?

4.    You chose a 1-year warmup, 2 years for calibration and 3 years for validation.  Are these lengths of time sufficient to include the extreme interannual variability that is typical of monsoon climates?

5.    The model sensitivity values are low.  Why? Important to include this topic in your discussion to help your readers have confidence in the model approach.  More generally, what is required to improve the precipitation estimates or their uncertainty?

6.    Your discussion really needs an introduction to tell your readers what they are going to read and how the topics are connected.

7.    Quite a few of the sentences in the Discussion repeat what the reader has already learned in the results and several add information that should be in the Introduction instead.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is written clearly and easy to read but major revisions are needed. So, in order to help the authors with some suggestions for improving their manuscript, I have provided a short non-all-inclusive list of general comments that I believe need to be carefully addressed and modifications made accordingly. 

The authors should spend more words. In the introduction, the authors should improve the state of the art with some more recent contributions available on the topic. Recent papers should be added(international relevance should enhance).

In Figure 6 I saw the term “evaporation” ET. How did the model consider it? Can you add some information about it?

There is a separate paragraph on “results" and "discussion”. Please add them together to better keep the attention of the readers, avoiding overlapping.

Add some information about the calibration of model parameters.

The authors should discuss also the uncertainty of model data (if can be significant and should be considered the unvertainty).

Finally, in the conclusion section, the limitations and recommendations of this research should be highlighted.

Best

Minor editing of English language required. There are some occasional grammatical problems within the text. It may need the attention of someone fluent in the English language to enhance the readability of the sentences.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The paper is improved. I think it is ready for the pubblication.